Final answer:
The Billroth I procedure is considered a partial gastrectomy, where part of the stomach is removed and the remainder is connected to the duodenum. Other procedures mentioned, like Whipple, Wertheim, and Zenker, are for different medical purposes. Proteins begin to be chemically digested in the stomach by the enzyme pepsin.
Step-by-step explanation:
The procedure described as a partial gastrectomy is Billroth I. This surgical procedure involves the removal of part of the stomach and then reattaching the remaining portion to the duodenum. This is often performed to treat ulcers or cancer by reducing the production of gastric acid and the overall size of the stomach.
In contrast, a Whipple procedure is a complex operation to remove the head of the pancreas, the first part of the small intestine (duodenum), the gallbladder, and a portion of the bile duct. The Wertheim procedure pertains to the radical surgery for cervical cancer. Zenker deals with a different part of the gastrointestinal tract, specifically, an esophageal disorder. Unlike these, the Roux-en-Y procedure is a type of weight-loss surgery where a small pouch is created from the stomach and connected directly to the small intestine (the jejunum), bypassing a large part of the stomach and the duodenum, which reduces food intake and nutrient absorption, effectively addressing obesity concerns.
Chemical digestion of proteins begins in the stomach, where pepsin, an enzyme, breaks down protein chains into smaller peptides. This process starts when pepsinogen, secreted by the gastric cells, is activated by the acidic environment of the stomach into pepsin.